Telephone-exchange system



H. G. WEBSTER.

TELEPHONE EXCHANGE SYSTEM.

APPLscATlor.' FILED MAR. 9l 1908.

Patented Aug. 15, 1922.

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H. G. WEBSTER.

VTELEPHNE EXCHANGi-SYSTEM. APPLICATION FILED IvIAII. 9, 190'8.

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H. G. WEBSTER.

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H.- G. WEBSTER. TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED MAR. 9, 1908.

Patented Aug. 15., 1922. E

`I4 SHEETS-SHEET \4.

H. G. WEBSTER.

TELEPHONE EXCHANGE SYSTEM.

APPLiCATlON FILED MAR. 9, 1908.

1,425,728. Patented Aug. 15,1922.

14 SHEETS-SHEET 5- @w www H. G. WEBSTER.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED MA-R. 9| |908..

Patented Aug. 15, 1922.

H. G. WEBSTER.

TELEPHONE EXCHANGE SYSTEM. APPLscATloN FILED MAR. 9, 190s.

1,425,728. l' PatentedAug. 15, 1922.

14 'sHEETs sHEET 1.

H. G. WEBSTER. l TELEPHONE EXCHANGE SYSTEIV..

APPLscATloN FILEDMAR. 9, 190s.

H. s. WEBSTER.

TELEPHONE EXCHANGE' SYSTEM.

APPLscATloN FILED MAR. 9, 190s.

'Lg Patented Aug. 15, 1922. l 14 SHEETS-SHEET 9. A N

H. G. WEBSTER. TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED MAR. 9| 1908.

1,425,728. Patented Aug. 15,1922,

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TILEPHONE EXCHANGE SYSTM.

APPLlcATloN FILED MAR.9.1908.

1,425,728. Patented Aug. 15, 1922.

14 SHEETS-SHEET Il.

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TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED MAR. 9, 190B.

Patented Aug. 15, 1922.

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H. G. WEBSTER.

TELEPHONE EXCHANGE SYSTEM.

APPLxcATloN FILED MAR. 9. 190s.

1,425,728. Patented'Aug. 15, 1922.

14 SHEETS-SHEET 13.

H. G. WEBSTER.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED MARKS, 1908. E

1,425,728; PatentedAug. 15,1922.

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HARRY G. WEBSTER. CHICAGO. ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TOKELLOGG SWITCHBOARD & SUPPLY COMPANY, A CORPORATION F ILLINOIS.

TELEPHONE-EXCHANGE SYSTEM.

Application led March 9,

To all who/1L f may conce/w.'

Be it known that I, HARRY (i. ins'rma residing in Chicago, in thecounty' of Cook and State ot' Illinois. have invented new and usefulImprovements in Telephone-Exchange Systems` of which the Afollowing is aspecitication.

My invention relates to systems in which selective switches are employedin building up the connections from the calling subscribers lilies tothe called subscribers` lines. and I employ, in organizing the systemot' my invention. selective switches divided into two general classes.First, what may be alled automat-ic switches which. when traveling. stopwhen engaging conductors of pre-determined electrical characters, nodirective impulses being employed for their operation: while switchesot' the second. class have the conductors associated with them. arrangedin different groups and are operated in response to directive impulsesto select a group ot' conductors. whereat'ter they are automaticallycontrolled to select contacts forming terminals of idle conductors.

Generally stated the object of my invention is to provide a telephoneexchange system in which connections are built up with `the aid ot'operators at one central otlice who, by suitable calling devices.control the directive switches to complete the desired connections. andin such system' toprovide an organization of co-operating automatic. anddirective switches ot' such character as t0 provide a relatively smallnumber of switches and conductors.

A further object of my invention is to pro-l vide means wherebysubscribers, whose lines terminate in exchanges at a distance from theexchange wherein the operators are located, may, by means of. two-wiretrunks extending` from their exchanges to the, operators exchange.manifest calls at the operators positions; and the operators working outover the'same trunks over which the calls came in may adjust directiveswitches at the branch exchanges to connect the calling lines with anydesired called lines and thereafter free the trunk lines for furtheruse, thus securing a desirable economy in the use of the trunk lines.

Other objects of the invention are to se cure certain more specificimprovements in the mechanism of the various switches employed and inthe circuits by which their adexchange.

Specification of Letters Patent. Patented Aug', 15, 1922,

190s. seriai No. 419,981.

justment is secured, together with certain improvements to be moreparticularly pointed out in the specific description and in the claims.

In describing my invention, I. shall assume a telephone system embracingseveral different exchanges located, it may be. in different sections ota large city, the 'exchanges being divided into two classes. First, a.class of main exchanges to which I shall refer as A exchanges, each suchexchange embracing a. large number of subscribers lines. In the systemas drawn out, the mechanism for each such A exchange is adapted for amaximum of 10,000 lines per Secondly, exchanges of a class which I shalldesignate B exchanges which may be branch exchanges having a relativelysmall number of subscribers each, the system as drawn out being arrangedfor a maximum of 1,000 subscribers per B ex- Y change.

rIhe various A and B exchanges being part of the same system, it isobvious that each subscriber must be enabled to secure connections tothesubscribers of his own main or A exchange and to the subscribers ofeach other main exchangeand also to the subscribers of each branch or Bexchange. Similarly, the B exchange subscribers must have facilities forsecuring connections to the subscribers of each A exchange and each Bexchange including subscribers of that B exchange in which their linesterminate.

In large telephone exchange systems of the character which I haveindicated, it has been found that a relatively small number of callsfrom any exchange are for subscribers of the same exchange; in fact, inlarge cities, the percentage of trunking callsto the total number ofcalls handledvvill amount to eighty per cent and Will sometimes run ashigh as ninety per cent. In .these systems, with the ordinary methods ofoperation, each trunking call requires the services of two operators,one in the originating exchange and one in the exchange in which thecalled subscribers line terminates. It is apparent that in the operationof such an exchange, the employment of tWo operators nfor eighty orninety per cent of the calls produces a very high charge for operatorsWages and Will a so rende-r the completionl of connections relativelyslovi7 and,

as has been demonstrated,vmuch more subject to error. thanin systemswhere but one operator is employed to complete eachgcon- .nection. Fromthese considerations, I have deemed it advisable, in -organizing'thesystem of my invention, to arrange the structure so that each call,whether from the subscriber of an A exchange, or from the subscriberofaB exchange, will be extended tof of maintaining a widely scattered corpsofworkers.

As will hereafter more fully appear, the

l trunk lines, which are employed between exchanges, are in each casecomposed of but two wires each, whether they beemployed as incomingtrunk lines oras outgoing trunk lines, and this is also true of thetrunk lines extending from the B exchanges, each of which is capable ofuse as an incoming trunk line or as an out-going trunk line, asrequired.

Referring tothe drawing, I show diagrammatically in Fig. 1 an Asubscribers substation connected with its line circuit at the exchange,together with circuits ofI an A line selector which makes connectionwith the line as a calling Aline, and the circuits of an A link selectorwhich is joined to the line selector and seeks out and makes connectionwith ya two-Wire trunk leading to the operators `exchange. The incomlngtrunks I have called A link trunks, and Fig. Qillustrates the circuitsof one of these, Fig. 2a showing the circuit arrangements of an impulsetransmitting device for use by the operator, while Fig. 2b is a planview of the keyboard of the same. In Fig. 3 I have illustrated thecircuits of a pair of A link connectors .which are automatic switchesconnected in parallel to an outgoing trunk line and serve, at the propertime, to connect a first selector, by means of an associated two-wire`trunk comprising conductors 177 and 178, with the out-going terminalsof the A linktrunk at the operators position. In Fig. 3a is shown an Alink connector connected to a B first selector. In Fig. 4, isillustrated an A first selector which is operated responsive todirective impulses trans.

mitted from 'an operators position to select a group of trunks assignedfor connection to the thousand lines among which the called line isincluded,l and then an idle trunk from a group, said A first selectorcorresponding circuits of one of said trunks.

to a certain extent to the first selectors known in purely automatictelephone systems. Fig. 4 illustrates a B first selector. Fig. 5illustrates an A second selector adapted for operation after theadjustment of the A first selector to select a group and then an idletrunk therefrom assigned for connections tothe hundred out of thepreviously se* lected thousand among which the called subscribers lineis located. In Fig. 6, are illus-Y trated circuits of a connector forselecting the tens and units of the called subscribers number, saidcircuits also comprising a party line switch for selectively ringing.the stations of a poly-station line. Fig. 7 illustrates a B secondselector for use in selecting B link trunks-that is, out-going trunks tothe B exchanges; Fig. 8 illustrating the Fig. 8a shows an operatorslink-circuit which I have designated the B cord trunk, together with thecircuits controlling a call signal for indicating nin-coming calls fromthe B exchange subscribers, said B cord trunk being employed forreceiving and completing the calls from B subscribers. In Fig. 9 Ihaveillustrated the circuits of a B third selector located at a B exchange;and in Fig. 10 I have illustrated the circuits of a B line connector,also located at a B exchange. In Fig. 11 I have illustrated themodification of the circuits of an A first selector; Fig. 12 showsmechanism that may be employed for the selective switches, said figurebeing a top view thereof; and Fig. 13 is a detailed view showing thearrangement of the switch wipers upon the switch shaft. Fig. 14 showsthe manner in which the figures are to be arranged for considering theoperation of a connection from an A subscriber to an A subscriber; Fig.15, the arrangement in which the figures are to be arranged inconsidering the connection from an A subscriber. to a B subscriber; Fig.16, the arrangement of the figures for connecting a B subscriber to an Asubscriber; Fig. 17, the arrangement for connecting a calling Bsubscriber in one B exchange to a called B subscriber in another Bexchange; and Fig. 18, the arrangement for connecting a calling Bsubscri er in a certain B exchange with a B called subscriber in thesame exchange. Fig. 19 is a skeleton view showing the generalorganization of the various mechanisms arranged in accordance with theinvention, and Fi 20 a similar view of a connection from a subscriber toanother B subscriber in the same exchange.

In organizing the system I have had in mind to reduce the operators workto a minimum in order that each operator may handle a maximum number 'ofcalls and the item of operators hire be correspondingly reduced. `Thusthe operators who receive calls from A exchange subscribers are re--quired only to ascertain the number of the subscriber desired and tothereupon press down a number of buttons of a keyboard associated withthe A link trunk upon which the call is manifested, the depression ofthe buttons counting out the number` of the called-for subscriber.Thereafter the operator has nothing to do with the connection. Theoperation of' adjusting the various switches to make connection with thecalled line, the ringing of the called subscriber, the transmission -ofthe busy signal back to the calling subscriber if the called line bebusy, and the restoration of the entire mechanism used in the connectionbeing automatically Controlled without requiring any attention whateverfrom the operator.

In the case of the operators who handle calls originating in the Bexchanges, the operator is required to insert a plug within aspring-jack of the B link trunk employed and then operate the properbuttons to count out the called subscribers number, and the operator isalso required, at the proper time, to Withdrawl the answering plug sheused.

Referring first to Fig. 19, the structural relation of the variousswitches will be more specifically referred to. At D 1 have indicated acalling subscriber-s station and line, said line being provided withpassive multiple called terminals at the le-ft and passive multiplecalling terminals at the right, said called terminals bei-ng preferablygrouped together with those of ninety-nine other lines before the wipersof a suitable number of connectors, and said calling terminals beinggrouped together with those of ninetynine other lines before the wipersof a suitable number of A line selectors, which may number ten for eachhundred lines. One of these 1 have indicated at E, and at G I haveindicated a master-switch whichis effective, when a call is initiatedover any line of the one hundred linegroup, to start an idle A lineselector E to seek out the multiple calling terminals of the callingline and to rest in connection with them. The A line selector E has itsA link selector Findividual to it, said A link selector being startedsimultaneously with the starting of the A line selector to seekoutmultiple terminals of an idle A link trunk leading to the operators eX-change.

It may be stated that, in Fig. 19, the automatic switches have beenindicated by circles with the conventional wiper symbol attached, whi'ethe directively operated switches have been indicated by squares withthe wipers Symbols. In the said Fig. 19, the trunk lines for which twoconductors only are required have been indicated by dotted lines.

The A link selector F may have before it the multiple contacts of onehundred A link trunks, which may extend to a number of operatorspositions vat the exchange. For

'sition begins to receive calls. Thus on the removal of the receiver atsubstation D, the

`A line selector, E, selects its line and the A link selector, F,selects a link circuit extending to an idle operators position; and whenthis connection is completed, a lamp associated with the A link trunk isdisplayed, and the operator inquires the number of the wantedsubscriber. Each A link -trunk preferably has its individual impulsetransmitting device which may consist of six rows of buttons, each rowconsisting of ten buttons, one for each of' the numbers from 1 to 9, anda button for the zero which is represented by ten impulses. The operatordepresses one button ineach of the first live rows to count out thecalled-for subscribers 'number and then depresses a button in the sixthrow which determines the exchange to which the A link trunk shall beextended and causes it to be connected over a twowire trunk of thatexchange, whereafter the five previously depressed buttons control meansfor counting out the number of the called-for subscriber by sets of.current impulses which adjust selective switches at the distant exchangeto complete the required connection.

Each out-going. A trunk is connected at its out-going end with anl Afirst selector N and at ,its answering end with an A link connector L,which latter has before it mul.- tiple terminals of one hundred A linktrunks. Each A link trunk has multiple terminals K before a number ofAvlink connectors L connected. to trunks extending to one distantexchange, a master-switch M being provided for the A link connectors Lfor one particular exchange, said masterswitch serving to start an idleA link connector to select multiple terminals of the A link trunk overwhich-a call is being extended. The A link trunk shown in Fig. 19 has,in addition to the` multiple terminals K which are selectable by anumber of A link connectors L connected to A first selectors N of asecond exchange, a masterswitch M being arranged to start an idle said Alilik connectors L2 will automatically seek out and connect with theterminals K2 ot' the A link trunk over which the call is beingcompleted.

It is thus apparent that 'each A link Ltrunk has a. number of groups ot'multiple terminals K. K. K2. etc.. and it will have as many such groups4as there are different exchanges. All of the said multiple terminalsare normally unselectable by the A link connectors L. L and L2respectively, having access to them, and the operator is enabled torender any group K or K or 1'2 selectable by its A link connectors.while leaving the other groups unselectable. For instance, to render thegroup K select-able` the operator may depress the button indicated atle., the depression of said button also operating the master-switchmechanism M to start an idle A link connector L to connectitstrunk tothe terminals K. now rendered selectable, of'the A link trunk. Thedepression of key k, however. has no eifect upon the terminals K and K2and they remain unselectable to their respective A link connectors. Onthe other hand. if the operator learns that the calling subscriber Ddesires to be connected with the line of a exchange, she will depressthe button 71.2 and this will render the multiple contacts K2 selectableand will influ.

ence the master-switch mechanism B 2. associated with the switches L2,to start one of them which will seek out and connect with the terminalK2,` the A link trunk being thus connected'with. aB first selector N2assigned for connection to the B exchanges. It is thus apparent that ifthe o )erator have ten buttonslzf, 71.2, h2, h4, etc.: slie may haveaccess to ten groups of A link comie-ctors by means of their respectiveten master-switches and may control distributively the selectablecondition of ten groups of multiple terminals all belonging tothe same Alink trunk. It will of course be understood that the master-switchmechanism M is not individual to a particular A link trunk` but that itis connected with branch wires to the but-- tons z. of one hundred Alink trunks appearing before different operatorsthat is, to as many Alink trunks as have multiple terminals before the master-switchs groupof A link connectors.

Assuming thatthe calling subscriber D desires to be connected tosubscriber D- namely, to a subscriber at a distant A exchange-theoperator will depress the buttons as described, corresponding to thedigits of the called number, the depression of button h. thereaftercausing a switch L to connect with its set of contacts K, whereafter thetransmission of the impulses will first adjust the A first selector N toselect the thousand, the next set will adjust the second selector 0 toselect the hundreds, the next set of impulses the connector .-P toselect the tens, and the next set the same switch P to select-the units,whereafter the fifth set of impulses adjust the party line switch P toselect the frequency of generator current to ring the called subscribersbell, whereafter the busy signal will betransmitted to substation D ifthe called line be`busy, or the bellof D rung if the called line beidle. Assuming the irst to be the case, subscriber D hearing the busysignal, replaces his receiver and his line and switches E, F, L, N, 0.P, P', are all restored to normal. s suming, however, that the calledsubscribers line is idle `and that he answersthe call, upon such answerthe power to restore the switches P and P is taken froml the callingsubscriber and turned t o the called subscriber so that when, at theconclusion of conversation, subscriber Dreplaces his receiver, theswitches P and P will be restored` the other switches being restoredwhen the calling subscriber hangs up.

Assuming, however, that the calling subscriber D desires to be connectedwith a subscriber in the B exchange, the operator would have depressedthe button 11,2, thus causing a switch L2 to select the terminals K2,whereat'ter the first set of impulses would adjust the B first selectorN2, which may have before it ten groups of multiple contacts of B secondselectors R, the B second selectors of each group being assigned forconnection to a dil-ferent group of ten B exchanges. Thus the B rstselector N2 is common for connection to a group of one hundred Bexchanges and is operated directively to select a groupl of ten and thenan idle second selector R out of the group of ten. The second selector Ris adjusted by the second set of impulses to select one of ten groups ofmultiple terminals of B link trunks, those of each group extending to adifferent B exchange, and then an idle B link trunk out of the selectedgroup so that the connection is extended over an idle B link trunk tothe wanted B exchange. At the B exchange, each trunk terminates in aswitch S which I have termed a B trunk controller and pair comprising aB third selector T and a B line connector U,the said switches T and U atthe branch exchanges being arranged in pairs, tb the end to behereinafter described.

It should be stated at this point that each third set of currentimpulses transmitted comprises one extra impulse-that is, .one impulsemore than there are units in the digit to be transmitted. This extraimpulse is for the purpose of operating the B trunk 'controller S, andthe A line connection P is arranged to take care of this additionalimpulse, without producing a wrong selection, by its Wipers being setback so that two imist pulses are required before the said A lineconnector P selects its first group ofcontacts.

The extra impulse reaching the B trunkpulses operates upon the mechanismof the third selector T to select a group of contactsforming terminalsof B line connectors U, assigned for connection to the hundredcorresponding to the wanted number. The fourth and fifth sets ofimpulses adjust the B line connector U to engagement with the multipleterminals of the calledfor line, whereafter the busy signal to thecalling subscriber, if the called line be busy, the ringing of thecalled-for subscriber, and the release of the mechanism, occur as in theprevious case. It is there fore seen that when the connection is beingextended to an A-called subscriber, the fifth or linal set of impulsesis used to adjust a party-line generator selecting switch, whereas whenconnectionv is extended to a B called subscriber, the fifth s et isemployed to adjust the connector itself.l This is believed to be a novelfeature.

As before stated, the B exchanges are preferably arranged each for onethousand lines, and the switches thereat include two classes ofdirectively operable switches, namely, B third selectors T, T', in Fig.19, and B line connectors Il, U. The switches at the B exchange alsoinclude two classes of automatically operated switches-namely,

B trunk controllers S, S, and a number of master-switches u.

At the B exchanges the lines are arranged, by having their multipleterminals grouped together, in groups of one hundred, according to theirnumerical values, and each group of lines may have ten or more. B lineconnectors U, each of which will be capable of making connection withmultiple terminals of any line of its appropriate group. There wouldthus be for4 one thousand lines ten groups of lines of one hundredeachand ten groups of ten or more line connectors, one for each group oflines. The said line connectors are arranged for a double use.

`They may beI either directively operated responsive to current impulsestransmitted over B link trunks, of they may be automatically operatedresponsive to the removal of a receiver at a. B exchange substation toconnect a B link trunk with a calling B exchange subsribers line. Forstarting the B line connectors, U, to connect with calling lines, themaster-switch, u, one for each group of lines, is so arranged that uponthe removal of the receiver, it will only start a B line connector, U,whose pairedB third selector, T, is at that time engaged by the B trunkcontroller, S, of an idle link trunk. When the B line connector hasselected a calling B exchange line, the connection over the B link trunkexists by way of a link permanently uniting its B third selector,

T, With'the B line connector, U, through the B trunk controller S thenengaging the terminals of switch, T, and over the trunk to the B cordtrunk operators position, where a signal is displayed and the operatoranswers by means of a cord connector. As soon as a B line connector isstarted in its automatic search of a calling line, the multipleterminals of the'B link trunk, whose B trunk controller S is engagingthe switch pair Whose switch, U, has started, are madel busy at the Bsecond selectors R at the operators exchange so that the trunk isinstantly guarded from seizure at the B second selectors. The call beingextended to the B operators exchange, thc oprator thereat may find thatthe calling subscriber desires his line to be connected with an Aexchange subscriber. Assuming this to be the case, the operator at the Bcord trunk position actuates buttons of her lcalling .device for thatcord to cause an A link selector L for the appropriate exchange toselect multiple terminals of the B cord trunk W- with which sheanswered, and the call is extended via the switch, L, the A firstselector, N, the second selector. O, the connector, P, and the partyline switch, P', just as be fore. The B cord trunk is provided with .twosupervisory signals,one controlled by the calling party and. onecontrolled by the called party. lVhen the called subscriber D2 replaceshis receiver, the switches P and P will be restored; and when thecalling B exchange subscriber V replaces his receiver, the B trunkcontroller S is movedof the switch T and the answering supervisory lampis displayed. Both lamps being now displayed, the operator withdraws theplug. The switches L, N and O are all restored to normal.

In Fig. 20, it is asumed that a calling subscriber 7 in a B exchange hasremoved his receiver, whereon the B line connector U selected themultipled terminal of the line and the call was extended over thepermanent link, associating switch U with switch T, to the B link trunkhaving the controller S then engaging switch T, and that the operator atthe B cord'trunk W Vanswered the call and ascertained that the calledsubscriber belonged to the same B exchange to which the callingsubscriber belonged. The operator at V thereupon connected her callingmechanism operatively with the answering end of her lcord trunk andactuated keys corresponding to the last three digits of the calledsubscribers number. She then depresses a special starting lector T andsweeps over its contacts, comingk called subscriber D2 will beautomatically rung or the busy signal extended. Immediately followingthe last impulse adjusting the B line connector U', the B trunkcontroller S of the B link trunk which was used, "is moved 'off theterminals of the B third seto rest engaging terminals of a B thirdselector T of an idle switch pair T, U, the B link trunk being thenready to be used for calls from or to subscribers of its vB exchange. InFig. 2O the talking circuit established from the calling subscriber, Vis shown by the heavily marked conductors extending through the switch,U, over its by-path to the switch, T, thence to a multiple contactforming a terminal of the connector, U',

and thence to the called subscriber, D2. When this connection isestablished, it is seen that the switch, T', of the pair, T', U', is notemployed in the connection at all. Neither can it be selected by a Blink trunk controller, S. Moreover, if at the time the switch Tattempted to select the switch U', a controller S- was resting on aterminal of the switch T', said switch T would he automatically movedaway from the terminaly thereof in Search of an unconnected idle switchpair T, U.l Thus for a connection of this character, the trunk to theoperators exchange is used `for a short time onlynamely, only longenough for the operator to receive the order and to transmit thedirective impulses back over the trunk. The -two subscribers V and D2,on re lacing their receivers, cause the switches, T, and U to berestored to normal, and the switch pairs may then be selected by a Btrunk controller, S.

It is apparent that in order to get Cthe fulluse out of the trunks, asufficient number of switch pairs, T, U, must be provided so that eachtrunk controller S, when moved ot terminals of a busy switch pair, mayviind terminals of an idle switch pair so that it f may come to restengaging them and so be available for use. The' switch pairs T, U, willtherefore exceed in number the number of B link trunks for the exchange.It will also be understood as being within the scope of the inventionthat switches of the general character of the B line connector, U, may

vbe provided without any individually asso- In developing the system, Ihave arranged for the use of rotary switches exclusively for both theautomatic and directive switches, the wipers or movable contacts beingdesignedto make a complete circular revolution from a normal pointaround 'to the same normal point when restoration is to be made, therotary movement being 'thus always in the same direction. For theautomatic switches, short steps of the wipers only are employed. Thus,assuming switches having one hundred contact sets arranged in a circle,the switch would comprise wipers mounted upon a rotary shaft, said shaftcarrying a ratchet provided with one hundred and one teeth and a magnetcontrolling an actuating pawl for driving the ratchet, shaft and wipers.In such case, one hundred ratchet teeth would be employed-for adjustingthe wipers to engage one hundred contact sets included in the switch,and the additional ratchet teeth above the one hundredwould be for thepurpose of bringing the wipers into the additional normal position, saidposition being one between the first contact set of the switch and theone hundredth contact Set.

In the case of the direct-ively operated switches, which are designed topermit of the selection of ten groups of contact sets, each groupcomp-rising ten contact sets, the contacts are arranged circularly, andthe wipers are mounted upon a rotary shaft as before, the so-calledprimary movements of the wipers to select the group! wanted beingeffected by long step-s, each long step causing the wipers to advance adistance corresponding to eleven short steps, the wipers for each longstep thus wiping over ten sets of contacts to a position between the setwiped over and the succeeding set. To select an individual idle contactset out of a selected group, the wipers are caused to make short steps,each such step being one-eleventh as long as the group-selecting steps,and each such Short step `moves the wipers from one contact set of agroup to the next contact set,

`moving continually until an idle set is selected.

For producing the long or group-selecting steps, one magnet is used,while for producing the short steps another magnet is employed. Both ofthese magnets are true driving magnets, and in no part of its operationis the switch actuated by a stored 'power controlled by escapements,although such method would be within the'scope of the invention. For thefirst selectors, second se-

